diff options
Diffstat (limited to 'compiler/rustc_monomorphize/src/partitioning')
| -rw-r--r-- | compiler/rustc_monomorphize/src/partitioning/default.rs | 644 | ||||
| -rw-r--r-- | compiler/rustc_monomorphize/src/partitioning/mod.rs | 673 |
2 files changed, 0 insertions, 1317 deletions
diff --git a/compiler/rustc_monomorphize/src/partitioning/default.rs b/compiler/rustc_monomorphize/src/partitioning/default.rs deleted file mode 100644 index 603b3ddc1..000000000 --- a/compiler/rustc_monomorphize/src/partitioning/default.rs +++ /dev/null @@ -1,644 +0,0 @@ -use std::cmp; -use std::collections::hash_map::Entry; - -use rustc_data_structures::fx::{FxHashMap, FxHashSet}; -use rustc_hir::def::DefKind; -use rustc_hir::def_id::{DefId, LOCAL_CRATE}; -use rustc_hir::definitions::DefPathDataName; -use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags; -use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel}; -use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, Linkage, Visibility}; -use rustc_middle::mir::mono::{InstantiationMode, MonoItem}; -use rustc_middle::ty::print::characteristic_def_id_of_type; -use rustc_middle::ty::{self, visit::TypeVisitableExt, InstanceDef, TyCtxt}; -use rustc_span::symbol::Symbol; - -use super::PartitioningCx; -use crate::collector::InliningMap; -use crate::partitioning::{MonoItemPlacement, Partition, PlacedRootMonoItems}; - -pub struct DefaultPartitioning; - -impl<'tcx> Partition<'tcx> for DefaultPartitioning { - fn place_root_mono_items<I>( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - mono_items: &mut I, - ) -> PlacedRootMonoItems<'tcx> - where - I: Iterator<Item = MonoItem<'tcx>>, - { - let mut roots = FxHashSet::default(); - let mut codegen_units = FxHashMap::default(); - let is_incremental_build = cx.tcx.sess.opts.incremental.is_some(); - let mut internalization_candidates = FxHashSet::default(); - - // Determine if monomorphizations instantiated in this crate will be made - // available to downstream crates. This depends on whether we are in - // share-generics mode and whether the current crate can even have - // downstream crates. - let export_generics = - cx.tcx.sess.opts.share_generics() && cx.tcx.local_crate_exports_generics(); - - let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx); - let cgu_name_cache = &mut FxHashMap::default(); - - for mono_item in mono_items { - match mono_item.instantiation_mode(cx.tcx) { - InstantiationMode::GloballyShared { .. } => {} - InstantiationMode::LocalCopy => continue, - } - - let characteristic_def_id = characteristic_def_id_of_mono_item(cx.tcx, mono_item); - let is_volatile = is_incremental_build && mono_item.is_generic_fn(); - - let codegen_unit_name = match characteristic_def_id { - Some(def_id) => compute_codegen_unit_name( - cx.tcx, - cgu_name_builder, - def_id, - is_volatile, - cgu_name_cache, - ), - None => fallback_cgu_name(cgu_name_builder), - }; - - let codegen_unit = codegen_units - .entry(codegen_unit_name) - .or_insert_with(|| CodegenUnit::new(codegen_unit_name)); - - let mut can_be_internalized = true; - let (linkage, visibility) = mono_item_linkage_and_visibility( - cx.tcx, - &mono_item, - &mut can_be_internalized, - export_generics, - ); - if visibility == Visibility::Hidden && can_be_internalized { - internalization_candidates.insert(mono_item); - } - - codegen_unit.items_mut().insert(mono_item, (linkage, visibility)); - roots.insert(mono_item); - } - - // Always ensure we have at least one CGU; otherwise, if we have a - // crate with just types (for example), we could wind up with no CGU. - if codegen_units.is_empty() { - let codegen_unit_name = fallback_cgu_name(cgu_name_builder); - codegen_units.insert(codegen_unit_name, CodegenUnit::new(codegen_unit_name)); - } - - let codegen_units = codegen_units.into_values().collect(); - PlacedRootMonoItems { codegen_units, roots, internalization_candidates } - } - - fn merge_codegen_units( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut Vec<CodegenUnit<'tcx>>, - ) { - assert!(cx.target_cgu_count >= 1); - - // Note that at this point in time the `codegen_units` here may not be - // in a deterministic order (but we know they're deterministically the - // same set). We want this merging to produce a deterministic ordering - // of codegen units from the input. - // - // Due to basically how we've implemented the merging below (merge the - // two smallest into each other) we're sure to start off with a - // deterministic order (sorted by name). This'll mean that if two cgus - // have the same size the stable sort below will keep everything nice - // and deterministic. - codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str())); - - // This map keeps track of what got merged into what. - let mut cgu_contents: FxHashMap<Symbol, Vec<Symbol>> = - codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name()])).collect(); - - // Merge the two smallest codegen units until the target size is - // reached. - while codegen_units.len() > cx.target_cgu_count { - // Sort small cgus to the back - codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate())); - let mut smallest = codegen_units.pop().unwrap(); - let second_smallest = codegen_units.last_mut().unwrap(); - - // Move the mono-items from `smallest` to `second_smallest` - second_smallest.modify_size_estimate(smallest.size_estimate()); - for (k, v) in smallest.items_mut().drain() { - second_smallest.items_mut().insert(k, v); - } - - // Record that `second_smallest` now contains all the stuff that was - // in `smallest` before. - let mut consumed_cgu_names = cgu_contents.remove(&smallest.name()).unwrap(); - cgu_contents.get_mut(&second_smallest.name()).unwrap().append(&mut consumed_cgu_names); - - debug!( - "CodegenUnit {} merged into CodegenUnit {}", - smallest.name(), - second_smallest.name() - ); - } - - let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx); - - if cx.tcx.sess.opts.incremental.is_some() { - // If we are doing incremental compilation, we want CGU names to - // reflect the path of the source level module they correspond to. - // For CGUs that contain the code of multiple modules because of the - // merging done above, we use a concatenation of the names of all - // contained CGUs. - let new_cgu_names: FxHashMap<Symbol, String> = cgu_contents - .into_iter() - // This `filter` makes sure we only update the name of CGUs that - // were actually modified by merging. - .filter(|(_, cgu_contents)| cgu_contents.len() > 1) - .map(|(current_cgu_name, cgu_contents)| { - let mut cgu_contents: Vec<&str> = - cgu_contents.iter().map(|s| s.as_str()).collect(); - - // Sort the names, so things are deterministic and easy to - // predict. We are sorting primitive `&str`s here so we can - // use unstable sort. - cgu_contents.sort_unstable(); - - (current_cgu_name, cgu_contents.join("--")) - }) - .collect(); - - for cgu in codegen_units.iter_mut() { - if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) { - if cx.tcx.sess.opts.unstable_opts.human_readable_cgu_names { - cgu.set_name(Symbol::intern(&new_cgu_name)); - } else { - // If we don't require CGU names to be human-readable, - // we use a fixed length hash of the composite CGU name - // instead. - let new_cgu_name = CodegenUnit::mangle_name(&new_cgu_name); - cgu.set_name(Symbol::intern(&new_cgu_name)); - } - } - } - } else { - // If we are compiling non-incrementally we just generate simple CGU - // names containing an index. - for (index, cgu) in codegen_units.iter_mut().enumerate() { - let numbered_codegen_unit_name = - cgu_name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index)); - cgu.set_name(numbered_codegen_unit_name); - } - } - } - - fn place_inlined_mono_items( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - roots: FxHashSet<MonoItem<'tcx>>, - ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement> { - let mut mono_item_placements = FxHashMap::default(); - - let single_codegen_unit = codegen_units.len() == 1; - - for old_codegen_unit in codegen_units.iter_mut() { - // Collect all items that need to be available in this codegen unit. - let mut reachable = FxHashSet::default(); - for root in old_codegen_unit.items().keys() { - follow_inlining(*root, cx.inlining_map, &mut reachable); - } - - let mut new_codegen_unit = CodegenUnit::new(old_codegen_unit.name()); - - // Add all monomorphizations that are not already there. - for mono_item in reachable { - if let Some(linkage) = old_codegen_unit.items().get(&mono_item) { - // This is a root, just copy it over. - new_codegen_unit.items_mut().insert(mono_item, *linkage); - } else { - if roots.contains(&mono_item) { - bug!( - "GloballyShared mono-item inlined into other CGU: \ - {:?}", - mono_item - ); - } - - // This is a CGU-private copy. - new_codegen_unit - .items_mut() - .insert(mono_item, (Linkage::Internal, Visibility::Default)); - } - - if !single_codegen_unit { - // If there is more than one codegen unit, we need to keep track - // in which codegen units each monomorphization is placed. - match mono_item_placements.entry(mono_item) { - Entry::Occupied(e) => { - let placement = e.into_mut(); - debug_assert!(match *placement { - MonoItemPlacement::SingleCgu { cgu_name } => { - cgu_name != new_codegen_unit.name() - } - MonoItemPlacement::MultipleCgus => true, - }); - *placement = MonoItemPlacement::MultipleCgus; - } - Entry::Vacant(e) => { - e.insert(MonoItemPlacement::SingleCgu { - cgu_name: new_codegen_unit.name(), - }); - } - } - } - } - - *old_codegen_unit = new_codegen_unit; - } - - return mono_item_placements; - - fn follow_inlining<'tcx>( - mono_item: MonoItem<'tcx>, - inlining_map: &InliningMap<'tcx>, - visited: &mut FxHashSet<MonoItem<'tcx>>, - ) { - if !visited.insert(mono_item) { - return; - } - - inlining_map.with_inlining_candidates(mono_item, |target| { - follow_inlining(target, inlining_map, visited); - }); - } - } - - fn internalize_symbols( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, - ) { - if codegen_units.len() == 1 { - // Fast path for when there is only one codegen unit. In this case we - // can internalize all candidates, since there is nowhere else they - // could be accessed from. - for cgu in codegen_units { - for candidate in &internalization_candidates { - cgu.items_mut().insert(*candidate, (Linkage::Internal, Visibility::Default)); - } - } - - return; - } - - // Build a map from every monomorphization to all the monomorphizations that - // reference it. - let mut accessor_map: FxHashMap<MonoItem<'tcx>, Vec<MonoItem<'tcx>>> = Default::default(); - cx.inlining_map.iter_accesses(|accessor, accessees| { - for accessee in accessees { - accessor_map.entry(*accessee).or_default().push(accessor); - } - }); - - // For each internalization candidates in each codegen unit, check if it is - // accessed from outside its defining codegen unit. - for cgu in codegen_units { - let home_cgu = MonoItemPlacement::SingleCgu { cgu_name: cgu.name() }; - - for (accessee, linkage_and_visibility) in cgu.items_mut() { - if !internalization_candidates.contains(accessee) { - // This item is no candidate for internalizing, so skip it. - continue; - } - debug_assert_eq!(mono_item_placements[accessee], home_cgu); - - if let Some(accessors) = accessor_map.get(accessee) { - if accessors - .iter() - .filter_map(|accessor| { - // Some accessors might not have been - // instantiated. We can safely ignore those. - mono_item_placements.get(accessor) - }) - .any(|placement| *placement != home_cgu) - { - // Found an accessor from another CGU, so skip to the next - // item without marking this one as internal. - continue; - } - } - - // If we got here, we did not find any accesses from other CGUs, - // so it's fine to make this monomorphization internal. - *linkage_and_visibility = (Linkage::Internal, Visibility::Default); - } - } - } -} - -fn characteristic_def_id_of_mono_item<'tcx>( - tcx: TyCtxt<'tcx>, - mono_item: MonoItem<'tcx>, -) -> Option<DefId> { - match mono_item { - MonoItem::Fn(instance) => { - let def_id = match instance.def { - ty::InstanceDef::Item(def) => def, - ty::InstanceDef::VTableShim(..) - | ty::InstanceDef::ReifyShim(..) - | ty::InstanceDef::FnPtrShim(..) - | ty::InstanceDef::ClosureOnceShim { .. } - | ty::InstanceDef::Intrinsic(..) - | ty::InstanceDef::DropGlue(..) - | ty::InstanceDef::Virtual(..) - | ty::InstanceDef::CloneShim(..) - | ty::InstanceDef::ThreadLocalShim(..) - | ty::InstanceDef::FnPtrAddrShim(..) => return None, - }; - - // If this is a method, we want to put it into the same module as - // its self-type. If the self-type does not provide a characteristic - // DefId, we use the location of the impl after all. - - if tcx.trait_of_item(def_id).is_some() { - let self_ty = instance.substs.type_at(0); - // This is a default implementation of a trait method. - return characteristic_def_id_of_type(self_ty).or(Some(def_id)); - } - - if let Some(impl_def_id) = tcx.impl_of_method(def_id) { - if tcx.sess.opts.incremental.is_some() - && tcx.trait_id_of_impl(impl_def_id) == tcx.lang_items().drop_trait() - { - // Put `Drop::drop` into the same cgu as `drop_in_place` - // since `drop_in_place` is the only thing that can - // call it. - return None; - } - - // When polymorphization is enabled, methods which do not depend on their generic - // parameters, but the self-type of their impl block do will fail to normalize. - if !tcx.sess.opts.unstable_opts.polymorphize || !instance.has_param() { - // This is a method within an impl, find out what the self-type is: - let impl_self_ty = tcx.subst_and_normalize_erasing_regions( - instance.substs, - ty::ParamEnv::reveal_all(), - tcx.type_of(impl_def_id), - ); - if let Some(def_id) = characteristic_def_id_of_type(impl_self_ty) { - return Some(def_id); - } - } - } - - Some(def_id) - } - MonoItem::Static(def_id) => Some(def_id), - MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.to_def_id()), - } -} - -fn compute_codegen_unit_name( - tcx: TyCtxt<'_>, - name_builder: &mut CodegenUnitNameBuilder<'_>, - def_id: DefId, - volatile: bool, - cache: &mut CguNameCache, -) -> Symbol { - // Find the innermost module that is not nested within a function. - let mut current_def_id = def_id; - let mut cgu_def_id = None; - // Walk backwards from the item we want to find the module for. - loop { - if current_def_id.is_crate_root() { - if cgu_def_id.is_none() { - // If we have not found a module yet, take the crate root. - cgu_def_id = Some(def_id.krate.as_def_id()); - } - break; - } else if tcx.def_kind(current_def_id) == DefKind::Mod { - if cgu_def_id.is_none() { - cgu_def_id = Some(current_def_id); - } - } else { - // If we encounter something that is not a module, throw away - // any module that we've found so far because we now know that - // it is nested within something else. - cgu_def_id = None; - } - - current_def_id = tcx.parent(current_def_id); - } - - let cgu_def_id = cgu_def_id.unwrap(); - - *cache.entry((cgu_def_id, volatile)).or_insert_with(|| { - let def_path = tcx.def_path(cgu_def_id); - - let components = def_path.data.iter().map(|part| match part.data.name() { - DefPathDataName::Named(name) => name, - DefPathDataName::Anon { .. } => unreachable!(), - }); - - let volatile_suffix = volatile.then_some("volatile"); - - name_builder.build_cgu_name(def_path.krate, components, volatile_suffix) - }) -} - -// Anything we can't find a proper codegen unit for goes into this. -fn fallback_cgu_name(name_builder: &mut CodegenUnitNameBuilder<'_>) -> Symbol { - name_builder.build_cgu_name(LOCAL_CRATE, &["fallback"], Some("cgu")) -} - -fn mono_item_linkage_and_visibility<'tcx>( - tcx: TyCtxt<'tcx>, - mono_item: &MonoItem<'tcx>, - can_be_internalized: &mut bool, - export_generics: bool, -) -> (Linkage, Visibility) { - if let Some(explicit_linkage) = mono_item.explicit_linkage(tcx) { - return (explicit_linkage, Visibility::Default); - } - let vis = mono_item_visibility(tcx, mono_item, can_be_internalized, export_generics); - (Linkage::External, vis) -} - -type CguNameCache = FxHashMap<(DefId, bool), Symbol>; - -fn static_visibility<'tcx>( - tcx: TyCtxt<'tcx>, - can_be_internalized: &mut bool, - def_id: DefId, -) -> Visibility { - if tcx.is_reachable_non_generic(def_id) { - *can_be_internalized = false; - default_visibility(tcx, def_id, false) - } else { - Visibility::Hidden - } -} - -fn mono_item_visibility<'tcx>( - tcx: TyCtxt<'tcx>, - mono_item: &MonoItem<'tcx>, - can_be_internalized: &mut bool, - export_generics: bool, -) -> Visibility { - let instance = match mono_item { - // This is pretty complicated; see below. - MonoItem::Fn(instance) => instance, - - // Misc handling for generics and such, but otherwise: - MonoItem::Static(def_id) => return static_visibility(tcx, can_be_internalized, *def_id), - MonoItem::GlobalAsm(item_id) => { - return static_visibility(tcx, can_be_internalized, item_id.owner_id.to_def_id()); - } - }; - - let def_id = match instance.def { - InstanceDef::Item(def_id) | InstanceDef::DropGlue(def_id, Some(_)) => def_id, - - // We match the visibility of statics here - InstanceDef::ThreadLocalShim(def_id) => { - return static_visibility(tcx, can_be_internalized, def_id); - } - - // These are all compiler glue and such, never exported, always hidden. - InstanceDef::VTableShim(..) - | InstanceDef::ReifyShim(..) - | InstanceDef::FnPtrShim(..) - | InstanceDef::Virtual(..) - | InstanceDef::Intrinsic(..) - | InstanceDef::ClosureOnceShim { .. } - | InstanceDef::DropGlue(..) - | InstanceDef::CloneShim(..) - | InstanceDef::FnPtrAddrShim(..) => return Visibility::Hidden, - }; - - // The `start_fn` lang item is actually a monomorphized instance of a - // function in the standard library, used for the `main` function. We don't - // want to export it so we tag it with `Hidden` visibility but this symbol - // is only referenced from the actual `main` symbol which we unfortunately - // don't know anything about during partitioning/collection. As a result we - // forcibly keep this symbol out of the `internalization_candidates` set. - // - // FIXME: eventually we don't want to always force this symbol to have - // hidden visibility, it should indeed be a candidate for - // internalization, but we have to understand that it's referenced - // from the `main` symbol we'll generate later. - // - // This may be fixable with a new `InstanceDef` perhaps? Unsure! - if tcx.lang_items().start_fn() == Some(def_id) { - *can_be_internalized = false; - return Visibility::Hidden; - } - - let is_generic = instance.substs.non_erasable_generics().next().is_some(); - - // Upstream `DefId` instances get different handling than local ones. - let Some(def_id) = def_id.as_local() else { - return if export_generics && is_generic { - // If it is an upstream monomorphization and we export generics, we must make - // it available to downstream crates. - *can_be_internalized = false; - default_visibility(tcx, def_id, true) - } else { - Visibility::Hidden - }; - }; - - if is_generic { - if export_generics { - if tcx.is_unreachable_local_definition(def_id) { - // This instance cannot be used from another crate. - Visibility::Hidden - } else { - // This instance might be useful in a downstream crate. - *can_be_internalized = false; - default_visibility(tcx, def_id.to_def_id(), true) - } - } else { - // We are not exporting generics or the definition is not reachable - // for downstream crates, we can internalize its instantiations. - Visibility::Hidden - } - } else { - // If this isn't a generic function then we mark this a `Default` if - // this is a reachable item, meaning that it's a symbol other crates may - // access when they link to us. - if tcx.is_reachable_non_generic(def_id.to_def_id()) { - *can_be_internalized = false; - debug_assert!(!is_generic); - return default_visibility(tcx, def_id.to_def_id(), false); - } - - // If this isn't reachable then we're gonna tag this with `Hidden` - // visibility. In some situations though we'll want to prevent this - // symbol from being internalized. - // - // There's two categories of items here: - // - // * First is weak lang items. These are basically mechanisms for - // libcore to forward-reference symbols defined later in crates like - // the standard library or `#[panic_handler]` definitions. The - // definition of these weak lang items needs to be referencable by - // libcore, so we're no longer a candidate for internalization. - // Removal of these functions can't be done by LLVM but rather must be - // done by the linker as it's a non-local decision. - // - // * Second is "std internal symbols". Currently this is primarily used - // for allocator symbols. Allocators are a little weird in their - // implementation, but the idea is that the compiler, at the last - // minute, defines an allocator with an injected object file. The - // `alloc` crate references these symbols (`__rust_alloc`) and the - // definition doesn't get hooked up until a linked crate artifact is - // generated. - // - // The symbols synthesized by the compiler (`__rust_alloc`) are thin - // veneers around the actual implementation, some other symbol which - // implements the same ABI. These symbols (things like `__rg_alloc`, - // `__rdl_alloc`, `__rde_alloc`, etc), are all tagged with "std - // internal symbols". - // - // The std-internal symbols here **should not show up in a dll as an - // exported interface**, so they return `false` from - // `is_reachable_non_generic` above and we'll give them `Hidden` - // visibility below. Like the weak lang items, though, we can't let - // LLVM internalize them as this decision is left up to the linker to - // omit them, so prevent them from being internalized. - let attrs = tcx.codegen_fn_attrs(def_id); - if attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) { - *can_be_internalized = false; - } - - Visibility::Hidden - } -} - -fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility { - if !tcx.sess.target.default_hidden_visibility { - return Visibility::Default; - } - - // Generic functions never have export-level C. - if is_generic { - return Visibility::Hidden; - } - - // Things with export level C don't get instantiated in - // downstream crates. - if !id.is_local() { - return Visibility::Hidden; - } - - // C-export level items remain at `Default`, all other internal - // items become `Hidden`. - match tcx.reachable_non_generics(id.krate).get(&id) { - Some(SymbolExportInfo { level: SymbolExportLevel::C, .. }) => Visibility::Default, - _ => Visibility::Hidden, - } -} diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs deleted file mode 100644 index d0b23ca9e..000000000 --- a/compiler/rustc_monomorphize/src/partitioning/mod.rs +++ /dev/null @@ -1,673 +0,0 @@ -//! Partitioning Codegen Units for Incremental Compilation -//! ====================================================== -//! -//! The task of this module is to take the complete set of monomorphizations of -//! a crate and produce a set of codegen units from it, where a codegen unit -//! is a named set of (mono-item, linkage) pairs. That is, this module -//! decides which monomorphization appears in which codegen units with which -//! linkage. The following paragraphs describe some of the background on the -//! partitioning scheme. -//! -//! The most important opportunity for saving on compilation time with -//! incremental compilation is to avoid re-codegenning and re-optimizing code. -//! Since the unit of codegen and optimization for LLVM is "modules" or, how -//! we call them "codegen units", the particulars of how much time can be saved -//! by incremental compilation are tightly linked to how the output program is -//! partitioned into these codegen units prior to passing it to LLVM -- -//! especially because we have to treat codegen units as opaque entities once -//! they are created: There is no way for us to incrementally update an existing -//! LLVM module and so we have to build any such module from scratch if it was -//! affected by some change in the source code. -//! -//! From that point of view it would make sense to maximize the number of -//! codegen units by, for example, putting each function into its own module. -//! That way only those modules would have to be re-compiled that were actually -//! affected by some change, minimizing the number of functions that could have -//! been re-used but just happened to be located in a module that is -//! re-compiled. -//! -//! However, since LLVM optimization does not work across module boundaries, -//! using such a highly granular partitioning would lead to very slow runtime -//! code since it would effectively prohibit inlining and other inter-procedure -//! optimizations. We want to avoid that as much as possible. -//! -//! Thus we end up with a trade-off: The bigger the codegen units, the better -//! LLVM's optimizer can do its work, but also the smaller the compilation time -//! reduction we get from incremental compilation. -//! -//! Ideally, we would create a partitioning such that there are few big codegen -//! units with few interdependencies between them. For now though, we use the -//! following heuristic to determine the partitioning: -//! -//! - There are two codegen units for every source-level module: -//! - One for "stable", that is non-generic, code -//! - One for more "volatile" code, i.e., monomorphized instances of functions -//! defined in that module -//! -//! In order to see why this heuristic makes sense, let's take a look at when a -//! codegen unit can get invalidated: -//! -//! 1. The most straightforward case is when the BODY of a function or global -//! changes. Then any codegen unit containing the code for that item has to be -//! re-compiled. Note that this includes all codegen units where the function -//! has been inlined. -//! -//! 2. The next case is when the SIGNATURE of a function or global changes. In -//! this case, all codegen units containing a REFERENCE to that item have to be -//! re-compiled. This is a superset of case 1. -//! -//! 3. The final and most subtle case is when a REFERENCE to a generic function -//! is added or removed somewhere. Even though the definition of the function -//! might be unchanged, a new REFERENCE might introduce a new monomorphized -//! instance of this function which has to be placed and compiled somewhere. -//! Conversely, when removing a REFERENCE, it might have been the last one with -//! that particular set of generic arguments and thus we have to remove it. -//! -//! From the above we see that just using one codegen unit per source-level -//! module is not such a good idea, since just adding a REFERENCE to some -//! generic item somewhere else would invalidate everything within the module -//! containing the generic item. The heuristic above reduces this detrimental -//! side-effect of references a little by at least not touching the non-generic -//! code of the module. -//! -//! A Note on Inlining -//! ------------------ -//! As briefly mentioned above, in order for LLVM to be able to inline a -//! function call, the body of the function has to be available in the LLVM -//! module where the call is made. This has a few consequences for partitioning: -//! -//! - The partitioning algorithm has to take care of placing functions into all -//! codegen units where they should be available for inlining. It also has to -//! decide on the correct linkage for these functions. -//! -//! - The partitioning algorithm has to know which functions are likely to get -//! inlined, so it can distribute function instantiations accordingly. Since -//! there is no way of knowing for sure which functions LLVM will decide to -//! inline in the end, we apply a heuristic here: Only functions marked with -//! `#[inline]` are considered for inlining by the partitioner. The current -//! implementation will not try to determine if a function is likely to be -//! inlined by looking at the functions definition. -//! -//! Note though that as a side-effect of creating a codegen units per -//! source-level module, functions from the same module will be available for -//! inlining, even when they are not marked `#[inline]`. - -mod default; - -use std::cmp; -use std::fs::{self, File}; -use std::io::{BufWriter, Write}; -use std::path::{Path, PathBuf}; - -use rustc_data_structures::fx::{FxHashMap, FxHashSet}; -use rustc_data_structures::sync; -use rustc_hir::def_id::{DefIdSet, LOCAL_CRATE}; -use rustc_middle::mir; -use rustc_middle::mir::mono::MonoItem; -use rustc_middle::mir::mono::{CodegenUnit, Linkage}; -use rustc_middle::query::Providers; -use rustc_middle::ty::print::with_no_trimmed_paths; -use rustc_middle::ty::TyCtxt; -use rustc_session::config::{DumpMonoStatsFormat, SwitchWithOptPath}; -use rustc_span::symbol::Symbol; - -use crate::collector::InliningMap; -use crate::collector::{self, MonoItemCollectionMode}; -use crate::errors::{ - CouldntDumpMonoStats, SymbolAlreadyDefined, UnknownCguCollectionMode, UnknownPartitionStrategy, -}; - -enum Partitioner { - Default(default::DefaultPartitioning), - // Other partitioning strategies can go here. - Unknown, -} - -impl<'tcx> Partition<'tcx> for Partitioner { - fn place_root_mono_items<I>( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - mono_items: &mut I, - ) -> PlacedRootMonoItems<'tcx> - where - I: Iterator<Item = MonoItem<'tcx>>, - { - match self { - Partitioner::Default(partitioner) => partitioner.place_root_mono_items(cx, mono_items), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn merge_codegen_units( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut Vec<CodegenUnit<'tcx>>, - ) { - match self { - Partitioner::Default(partitioner) => partitioner.merge_codegen_units(cx, codegen_units), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn place_inlined_mono_items( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - roots: FxHashSet<MonoItem<'tcx>>, - ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement> { - match self { - Partitioner::Default(partitioner) => { - partitioner.place_inlined_mono_items(cx, codegen_units, roots) - } - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } - - fn internalize_symbols( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, - ) { - match self { - Partitioner::Default(partitioner) => partitioner.internalize_symbols( - cx, - codegen_units, - mono_item_placements, - internalization_candidates, - ), - Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy), - } - } -} - -struct PartitioningCx<'a, 'tcx> { - tcx: TyCtxt<'tcx>, - target_cgu_count: usize, - inlining_map: &'a InliningMap<'tcx>, -} - -pub struct PlacedRootMonoItems<'tcx> { - codegen_units: Vec<CodegenUnit<'tcx>>, - roots: FxHashSet<MonoItem<'tcx>>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, -} - -trait Partition<'tcx> { - fn place_root_mono_items<I>( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - mono_items: &mut I, - ) -> PlacedRootMonoItems<'tcx> - where - I: Iterator<Item = MonoItem<'tcx>>; - - fn merge_codegen_units( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut Vec<CodegenUnit<'tcx>>, - ); - - fn place_inlined_mono_items( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - roots: FxHashSet<MonoItem<'tcx>>, - ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement>; - - fn internalize_symbols( - &mut self, - cx: &PartitioningCx<'_, 'tcx>, - codegen_units: &mut [CodegenUnit<'tcx>], - mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>, - internalization_candidates: FxHashSet<MonoItem<'tcx>>, - ); -} - -fn get_partitioner(tcx: TyCtxt<'_>) -> Partitioner { - let strategy = match &tcx.sess.opts.unstable_opts.cgu_partitioning_strategy { - None => "default", - Some(s) => &s[..], - }; - - match strategy { - "default" => Partitioner::Default(default::DefaultPartitioning), - _ => Partitioner::Unknown, - } -} - -fn partition<'tcx, I>( - tcx: TyCtxt<'tcx>, - mono_items: &mut I, - max_cgu_count: usize, - inlining_map: &InliningMap<'tcx>, -) -> Vec<CodegenUnit<'tcx>> -where - I: Iterator<Item = MonoItem<'tcx>>, -{ - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning"); - - let mut partitioner = get_partitioner(tcx); - let cx = &PartitioningCx { tcx, target_cgu_count: max_cgu_count, inlining_map }; - // In the first step, we place all regular monomorphizations into their - // respective 'home' codegen unit. Regular monomorphizations are all - // functions and statics defined in the local crate. - let PlacedRootMonoItems { mut codegen_units, roots, internalization_candidates } = { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_roots"); - partitioner.place_root_mono_items(cx, mono_items) - }; - - for cgu in &mut codegen_units { - cgu.create_size_estimate(tcx); - } - - debug_dump(tcx, "INITIAL PARTITIONING", &codegen_units); - - // Merge until we have at most `max_cgu_count` codegen units. - // `merge_codegen_units` is responsible for updating the CGU size - // estimates. - { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_merge_cgus"); - partitioner.merge_codegen_units(cx, &mut codegen_units); - debug_dump(tcx, "POST MERGING", &codegen_units); - } - - // In the next step, we use the inlining map to determine which additional - // monomorphizations have to go into each codegen unit. These additional - // monomorphizations can be drop-glue, functions from external crates, and - // local functions the definition of which is marked with `#[inline]`. - let mono_item_placements = { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items"); - partitioner.place_inlined_mono_items(cx, &mut codegen_units, roots) - }; - - for cgu in &mut codegen_units { - cgu.create_size_estimate(tcx); - } - - debug_dump(tcx, "POST INLINING", &codegen_units); - - // Next we try to make as many symbols "internal" as possible, so LLVM has - // more freedom to optimize. - if !tcx.sess.link_dead_code() { - let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols"); - partitioner.internalize_symbols( - cx, - &mut codegen_units, - mono_item_placements, - internalization_candidates, - ); - } - - let instrument_dead_code = - tcx.sess.instrument_coverage() && !tcx.sess.instrument_coverage_except_unused_functions(); - - if instrument_dead_code { - assert!( - codegen_units.len() > 0, - "There must be at least one CGU that code coverage data can be generated in." - ); - - // Find the smallest CGU that has exported symbols and put the dead - // function stubs in that CGU. We look for exported symbols to increase - // the likelihood the linker won't throw away the dead functions. - // FIXME(#92165): In order to truly resolve this, we need to make sure - // the object file (CGU) containing the dead function stubs is included - // in the final binary. This will probably require forcing these - // function symbols to be included via `-u` or `/include` linker args. - let mut cgus: Vec<_> = codegen_units.iter_mut().collect(); - cgus.sort_by_key(|cgu| cgu.size_estimate()); - - let dead_code_cgu = - if let Some(cgu) = cgus.into_iter().rev().find(|cgu| { - cgu.items().iter().any(|(_, (linkage, _))| *linkage == Linkage::External) - }) { - cgu - } else { - // If there are no CGUs that have externally linked items, - // then we just pick the first CGU as a fallback. - &mut codegen_units[0] - }; - dead_code_cgu.make_code_coverage_dead_code_cgu(); - } - - // Finally, sort by codegen unit name, so that we get deterministic results. - codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str())); - - debug_dump(tcx, "FINAL", &codegen_units); - - codegen_units -} - -/// For symbol internalization, we need to know whether a symbol/mono-item is -/// accessed from outside the codegen unit it is defined in. This type is used -/// to keep track of that. -#[derive(Clone, PartialEq, Eq, Debug)] -enum MonoItemPlacement { - SingleCgu { cgu_name: Symbol }, - MultipleCgus, -} - -fn debug_dump<'a, 'tcx: 'a>(tcx: TyCtxt<'tcx>, label: &str, cgus: &[CodegenUnit<'tcx>]) { - let dump = move || { - use std::fmt::Write; - - let num_cgus = cgus.len(); - let max = cgus.iter().map(|cgu| cgu.size_estimate()).max().unwrap(); - let min = cgus.iter().map(|cgu| cgu.size_estimate()).min().unwrap(); - let ratio = max as f64 / min as f64; - - let s = &mut String::new(); - let _ = writeln!( - s, - "{label} ({num_cgus} CodegenUnits, max={max}, min={min}, max/min={ratio:.1}):" - ); - for cgu in cgus { - let _ = - writeln!(s, "CodegenUnit {} estimated size {}:", cgu.name(), cgu.size_estimate()); - - for (mono_item, linkage) in cgu.items() { - let symbol_name = mono_item.symbol_name(tcx).name; - let symbol_hash_start = symbol_name.rfind('h'); - let symbol_hash = symbol_hash_start.map_or("<no hash>", |i| &symbol_name[i..]); - - let _ = with_no_trimmed_paths!(writeln!( - s, - " - {} [{:?}] [{}] estimated size {}", - mono_item, - linkage, - symbol_hash, - mono_item.size_estimate(tcx) - )); - } - - let _ = writeln!(s); - } - - std::mem::take(s) - }; - - debug!("{}", dump()); -} - -#[inline(never)] // give this a place in the profiler -fn assert_symbols_are_distinct<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, mono_items: I) -where - I: Iterator<Item = &'a MonoItem<'tcx>>, - 'tcx: 'a, -{ - let _prof_timer = tcx.prof.generic_activity("assert_symbols_are_distinct"); - - let mut symbols: Vec<_> = - mono_items.map(|mono_item| (mono_item, mono_item.symbol_name(tcx))).collect(); - - symbols.sort_by_key(|sym| sym.1); - - for &[(mono_item1, ref sym1), (mono_item2, ref sym2)] in symbols.array_windows() { - if sym1 == sym2 { - let span1 = mono_item1.local_span(tcx); - let span2 = mono_item2.local_span(tcx); - - // Deterministically select one of the spans for error reporting - let span = match (span1, span2) { - (Some(span1), Some(span2)) => { - Some(if span1.lo().0 > span2.lo().0 { span1 } else { span2 }) - } - (span1, span2) => span1.or(span2), - }; - - tcx.sess.emit_fatal(SymbolAlreadyDefined { span, symbol: sym1.to_string() }); - } - } -} - -fn collect_and_partition_mono_items(tcx: TyCtxt<'_>, (): ()) -> (&DefIdSet, &[CodegenUnit<'_>]) { - let collection_mode = match tcx.sess.opts.unstable_opts.print_mono_items { - Some(ref s) => { - let mode = s.to_lowercase(); - let mode = mode.trim(); - if mode == "eager" { - MonoItemCollectionMode::Eager - } else { - if mode != "lazy" { - tcx.sess.emit_warning(UnknownCguCollectionMode { mode }); - } - - MonoItemCollectionMode::Lazy - } - } - None => { - if tcx.sess.link_dead_code() { - MonoItemCollectionMode::Eager - } else { - MonoItemCollectionMode::Lazy - } - } - }; - - let (items, inlining_map) = collector::collect_crate_mono_items(tcx, collection_mode); - - tcx.sess.abort_if_errors(); - - let (codegen_units, _) = tcx.sess.time("partition_and_assert_distinct_symbols", || { - sync::join( - || { - let mut codegen_units = partition( - tcx, - &mut items.iter().copied(), - tcx.sess.codegen_units(), - &inlining_map, - ); - codegen_units[0].make_primary(); - &*tcx.arena.alloc_from_iter(codegen_units) - }, - || assert_symbols_are_distinct(tcx, items.iter()), - ) - }); - - if tcx.prof.enabled() { - // Record CGU size estimates for self-profiling. - for cgu in codegen_units { - tcx.prof.artifact_size( - "codegen_unit_size_estimate", - cgu.name().as_str(), - cgu.size_estimate() as u64, - ); - } - } - - let mono_items: DefIdSet = items - .iter() - .filter_map(|mono_item| match *mono_item { - MonoItem::Fn(ref instance) => Some(instance.def_id()), - MonoItem::Static(def_id) => Some(def_id), - _ => None, - }) - .collect(); - - // Output monomorphization stats per def_id - if let SwitchWithOptPath::Enabled(ref path) = tcx.sess.opts.unstable_opts.dump_mono_stats { - if let Err(err) = - dump_mono_items_stats(tcx, &codegen_units, path, tcx.crate_name(LOCAL_CRATE)) - { - tcx.sess.emit_fatal(CouldntDumpMonoStats { error: err.to_string() }); - } - } - - if tcx.sess.opts.unstable_opts.print_mono_items.is_some() { - let mut item_to_cgus: FxHashMap<_, Vec<_>> = Default::default(); - - for cgu in codegen_units { - for (&mono_item, &linkage) in cgu.items() { - item_to_cgus.entry(mono_item).or_default().push((cgu.name(), linkage)); - } - } - - let mut item_keys: Vec<_> = items - .iter() - .map(|i| { - let mut output = with_no_trimmed_paths!(i.to_string()); - output.push_str(" @@"); - let mut empty = Vec::new(); - let cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty); - cgus.sort_by_key(|(name, _)| *name); - cgus.dedup(); - for &(ref cgu_name, (linkage, _)) in cgus.iter() { - output.push(' '); - output.push_str(cgu_name.as_str()); - - let linkage_abbrev = match linkage { - Linkage::External => "External", - Linkage::AvailableExternally => "Available", - Linkage::LinkOnceAny => "OnceAny", - Linkage::LinkOnceODR => "OnceODR", - Linkage::WeakAny => "WeakAny", - Linkage::WeakODR => "WeakODR", - Linkage::Appending => "Appending", - Linkage::Internal => "Internal", - Linkage::Private => "Private", - Linkage::ExternalWeak => "ExternalWeak", - Linkage::Common => "Common", - }; - - output.push('['); - output.push_str(linkage_abbrev); - output.push(']'); - } - output - }) - .collect(); - - item_keys.sort(); - - for item in item_keys { - println!("MONO_ITEM {item}"); - } - } - - (tcx.arena.alloc(mono_items), codegen_units) -} - -/// Outputs stats about instantiation counts and estimated size, per `MonoItem`'s -/// def, to a file in the given output directory. -fn dump_mono_items_stats<'tcx>( - tcx: TyCtxt<'tcx>, - codegen_units: &[CodegenUnit<'tcx>], - output_directory: &Option<PathBuf>, - crate_name: Symbol, -) -> Result<(), Box<dyn std::error::Error>> { - let output_directory = if let Some(ref directory) = output_directory { - fs::create_dir_all(directory)?; - directory - } else { - Path::new(".") - }; - - let format = tcx.sess.opts.unstable_opts.dump_mono_stats_format; - let ext = format.extension(); - let filename = format!("{crate_name}.mono_items.{ext}"); - let output_path = output_directory.join(&filename); - let file = File::create(&output_path)?; - let mut file = BufWriter::new(file); - - // Gather instantiated mono items grouped by def_id - let mut items_per_def_id: FxHashMap<_, Vec<_>> = Default::default(); - for cgu in codegen_units { - for (&mono_item, _) in cgu.items() { - // Avoid variable-sized compiler-generated shims - if mono_item.is_user_defined() { - items_per_def_id.entry(mono_item.def_id()).or_default().push(mono_item); - } - } - } - - #[derive(serde::Serialize)] - struct MonoItem { - name: String, - instantiation_count: usize, - size_estimate: usize, - total_estimate: usize, - } - - // Output stats sorted by total instantiated size, from heaviest to lightest - let mut stats: Vec<_> = items_per_def_id - .into_iter() - .map(|(def_id, items)| { - let name = with_no_trimmed_paths!(tcx.def_path_str(def_id)); - let instantiation_count = items.len(); - let size_estimate = items[0].size_estimate(tcx); - let total_estimate = instantiation_count * size_estimate; - MonoItem { name, instantiation_count, size_estimate, total_estimate } - }) - .collect(); - stats.sort_unstable_by_key(|item| cmp::Reverse(item.total_estimate)); - - if !stats.is_empty() { - match format { - DumpMonoStatsFormat::Json => serde_json::to_writer(file, &stats)?, - DumpMonoStatsFormat::Markdown => { - writeln!( - file, - "| Item | Instantiation count | Estimated Cost Per Instantiation | Total Estimated Cost |" - )?; - writeln!(file, "| --- | ---: | ---: | ---: |")?; - - for MonoItem { name, instantiation_count, size_estimate, total_estimate } in stats { - writeln!( - file, - "| `{name}` | {instantiation_count} | {size_estimate} | {total_estimate} |" - )?; - } - } - } - } - - Ok(()) -} - -fn codegened_and_inlined_items(tcx: TyCtxt<'_>, (): ()) -> &DefIdSet { - let (items, cgus) = tcx.collect_and_partition_mono_items(()); - let mut visited = DefIdSet::default(); - let mut result = items.clone(); - - for cgu in cgus { - for (item, _) in cgu.items() { - if let MonoItem::Fn(ref instance) = item { - let did = instance.def_id(); - if !visited.insert(did) { - continue; - } - let body = tcx.instance_mir(instance.def); - for block in body.basic_blocks.iter() { - for statement in &block.statements { - let mir::StatementKind::Coverage(_) = statement.kind else { continue }; - let scope = statement.source_info.scope; - if let Some(inlined) = scope.inlined_instance(&body.source_scopes) { - result.insert(inlined.def_id()); - } - } - } - } - } - } - - tcx.arena.alloc(result) -} - -pub fn provide(providers: &mut Providers) { - providers.collect_and_partition_mono_items = collect_and_partition_mono_items; - providers.codegened_and_inlined_items = codegened_and_inlined_items; - - providers.is_codegened_item = |tcx, def_id| { - let (all_mono_items, _) = tcx.collect_and_partition_mono_items(()); - all_mono_items.contains(&def_id) - }; - - providers.codegen_unit = |tcx, name| { - let (_, all) = tcx.collect_and_partition_mono_items(()); - all.iter() - .find(|cgu| cgu.name() == name) - .unwrap_or_else(|| panic!("failed to find cgu with name {name:?}")) - }; -} |